ELFDRV1 - Stepper Driver Rev 1.0 ELFDRV1 stepper driver - electroFUN LTD 1 © 2012 electroFUN LTD Stepper Driver - ELFDRV1 by F. Malpartida is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. Based on a work at http://www.electrofunltd.com ELFDRV1 stepper driver - electroFUN LTD 2 BRIEF The ELFDRV1 stepper motor driver carrier is an easy-to-use performant bipolar microstepping motor driver. The driver features adjustable current limiting, over current protection, and 4 different configurable micro-step resolutions. It operates from 8 V – 35 V and can deliver up to 2.5 A per coil. Fitted with external diodes to improve the over all thermal dissipation of the driver. Description The ELFDRV1 is a compact carrier board or breakout board for TI's DRV8818 Microstepping Driver with Indexer and over-current protection for driving stepper motors. This stepper driver lets you control one bipolar stepper motor up to 2.5 A per winding. Please refer to the heat dissipation section of this manual for optimum performance. ELFDRV1 stepper driver - electroFUN LTD 3 Features F EATURES 1. Just two control interface pins for step and direction. 2. One interface pin to enable the driver. 3. Four different step resolutions jumper configurable: full-step, 1/2, 1/4, 1/8. 4. Adjustable current control lets you set the maximum current output with a potentiometer, allowing you to use a wide range of supply voltages well above your stepper motor’s rated voltage. This will protect you motor and will enable you to achieve higher step rates. 5. Selectable decay modes using built in jumpers: slow decay, fast decay or mixed decay. Mixed decay provides a more intelligent chopping control by selecting the correct current decay mode automatically (board default). 6. Board has been designed for vertical mounting for optimum cooling under high current needs. In addition is occupies less space on your final project. The ELFDRV1 ships with all SMD components soldered on board, tested and with a set of header pins for you to solder. We also have an Arduino (UNO Rev 3 and Leonardo) or vinciDuino daughter board (shield) that can host up to 3 ELFDRV1s, making it an ideal and compact solution for driving a CNC machine. Please refer to the ELFSHL1. ELFDRV1 stepper driver - electroFUN LTD 4 Specifications Dimensions Size: 43mm x 33 mm Weight: 6g General specifications Motor driver: DRV8818 Logic operating voltage range: 3 V - 5.5V Motor driver operating voltage range: 8 V - 35 V Continuous output current per phase: up to 2.5 A Min step pulse duration: 1us PCB: FR4, 35um copper white solder resist 1.6 mm ELFDRV1 stepper driver - electroFUN LTD 5 USER GUIDE C ONFIGURATION AND U SAGE 1. Using the Driver 2. Power pin connection and wiring 3. Driver Configuration 4. Driver Control 5. Thermal Considerations Using the driver The driver has been designed for minimum configuration and external control from an MCU, just a simple step command (HIGH-LOW pulse) on the STP pin and a direction pin, DIR, HIGH or LOW to turn the motor clockwise or anti-clockwise. A simple *EN pin (active low) will enable or disable the ELFDRV1 output drivers. The driver comes pre-configured to work in mixed decay mode, giving a more flexible configuration for its current recirculation. The driver is configured in 1/8 step mode and can easily be reconfigured using 2 solder jumpers. Minimal wiring diagram for connecting a microcontroller to the ELFDRV1 stepper motor driver carrier. ELFDRV1 stepper driver - electroFUN LTD 6 ELFDRV1 stepper driver supply rails supply rails MCU IO control lines supply rails: VMOT: 8 V to 35 V - marked as 12 V on the PCB. Vcc: 3 V to 5.5 V - marked as 5 V on the PCB. GND: common ground between supply rails. MCU IO control lines: EN* = active low DIR = HIGH or LOW - CW, ACW STP = HIGH + LOW pulse ELFDRV1 stepper driver - electroFUN LTD 7 Power connections The driver requires a logic supply voltage (3 V – 5.5 V) to be connected across the Vcc and GND pins and a motor supply voltage of (8 V – 35 V) to be connected across VMOT and GND. VMOT supply should have appropriate decoupling capacitors close to the board (if using the CNC stepper mother board - ELFSHL1 shield - VMOT bypass capacitor is already fitted). Supply connectors VMOT +5V GND VMOT: Motor driver voltage - 8 V to 35 V pin GND: ground reference pin +5V: logic supply for the driver Warning: This driver board uses low-ESR ceramic capacitors, which makes it susceptible to LC voltage spikes. At times, these spikes can well exceed the 35 V maximum voltage rating for the DRV8818 and can permanently damage the driver (even when the motor supply voltage is as low as 12 V). One way to protect the driver from such LC voltage spikes is to place a large (>= 47uF) electrolytic cap on the +12V power rail. ELFDRV1 stepper driver - electroFUN LTD 8 Motor Connections ELFDRV1 stepper driver motor connections bipolar motor unipolar motor bipolar motor are connected directly to the driver. Ensure that phases coincide. unipolar motors with 6 and 8 wires can be connected to the driver as if they were bipolar motors. The center tap A COM can be connected instead of A’ to reduce the inductance, you will be able to get higher step orders while sacrificing torque. Warning: Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver (in general, rewiring anything while it is powered is asking for trouble). ELFDRV1 stepper driver - electroFUN LTD 9 Driver Configuration micro-stepping Most stepper motors have a step size of 1.8° or 200 steps per revolution. This is the step resolution that would be achieved when the driver is configured in full step mode. This micro-stepping driver allows for higher step resolutions. This is managed internally by the DRV8818 by energizing the coils with intermediate current levels. Step resolution for 200 steps per revolution motor: Full step: 200 steps per revolution / 1.8° 1/2: 400 steps per revolution / 0.9° 1/4: 800 steps per revolution / 0.45° 1/8: 1600 steps per revolution / 0.225° micro-stepping jumper configuration - bottom board view micro-stepping configuration The step size can be configured using the built-in jumpers, which can be found at the back of the board. The board is configured in 1/8 of a step, with jumpers on uSTEP configured to USM0 = 1 and USM1 = 1, by default. ELFDRV1 stepper driver - electroFUN LTD 10 Current limiting To achieve higher step rates, the motor supply should be much higher than would be permissible without active current limiting (current chopping). For example, most stepper motor specify what their maximum current ratings and coil resistence is as opposed to their rated voltage. This is because they specify the current rating at which the motor coils are rated If we consider a typical 2A stepper motor with a 2.5Ω coil resistance, it would indicate a maximum motor supply of 5 V. However, if we want to achieve higher step rates, we would need to energize the coils quicker by simply raising the voltage to 12 V (for example). However, we should be actively limiting the current to be under 2 A to prevent damage to the motor’s coils. The ELFDRV1 is based on TI’s DRV8818 which supports such active current limiting. It is configured using the onboard trimmer potentiometer. Current setting potentiometer P1 - test point Current Adjust Pot The easiest way to configure the output current per phase, is to power the board with a 5V supply (or the voltage you are going to use on your project) using the +5V and GND pins. Measure the voltage on test point P1 (please refer to image) and adjust the potentiometer. The coil current is calculated as follow: I(C) = V(P1)/0.8 ELFDRV1 stepper driver - electroFUN LTD 11 For example, to achieve a 1A coil current, you should adjust the potentiometer till you read 0.8 V on test point P1. By default, the board is configured to deliver 1 A per phase (trimmed using +5V on Vcc). Warning: do not exceed to 2.5 A maximum current rating of the board. It will get very hot and continuos usage beyond the 2.5A rating will cause permanent damage to the driver. This is the same as saying, never exceed V(P1) = 2 V when the board is in use in your project. Decay mode configuration The decay mode can be configured by using a simple solder jumper. By default (solder jumper completely open) it is configured in mixed decay mode. In mixed decay mode, the driver automatically selects the best coil discharge mechanism at a particular instant in time (slow or fast decay). This is what we call automatic discharge selection. If you are doing micro-stepping mixed decay mode is the only way to go. Decay mode configuration Fast decay Slow decay If you don’t know what decay mode is, please leave the default configuration. ELFDRV1 stepper driver - electroFUN LTD 12 Driver Control Each pulse to the STP input corresponds to one micro-step of the stepper motor in the direction selected by the DIR pin. These pins need to be actively driven and should not be left floating. Should you wish to only have the motor turning in only one direction, you can tie the DIR pin to Vcc or GND. Driver board control pins Direction pin Step pin Enable pin You will also need to control the *EN pin of the board to activate the output drivers of the DRV8818. The pulse (high-low cycle) on the STP pin should have a duration of at least 1us. ELFDRV1 stepper driver - electroFUN LTD 13 Thermal Considerations The DRV8818 ASIC, and hence the ELFDRV1, driver has a maximum current rating of 2.5 A per phase. The actual current it can deliver depends very much on how well you cool the DRV8818. Care has been taken when designing the circuit board to allow regular operation up to 1.5 A per phase. However, the actual current you can deliver the motor depends on how well you can keep the DRV8811 cool. We have achieved 2 A sustained operation with a heat sink and 2.5 A with a heat sink and forced air cooling. ELFDRV1 stepper driver - electroFUN LTD 14 HARDWARE H ARDWARE FILES 1. Schematic 2. Board layout 3. Board dimensions Main hardware related section with the board schematics, board layout and components, mechanical drawings with board dimensions. Original files can be download from www.electrofunLTD.com ELFDRV1 stepper driver - electroFUN LTD 15 Schematic ELFDRV1 stepper driver - electroFUN LTD 16 Board Layout ELFDRV1 - stepper driver board layout Components Part C1, C2, C3 C4, C5 C6, C7, C10 C8, C9 CUR_S D1 - D8 IC1 JP1 JP2 L1, L3 L2, L4 R1 - R2 R3, R5 - R9 R4 Value 0.22uF 1nF 0.1uF 10uF 10K diode DRV8818 IN MOT Green Red 0.1R 22K 2k2 Package C0805 C0805 C0805 A/3216-18R TRIMPOT_BOURNS3MM SOD-128 HTSSOP28PWP MOLEX-1X6 MOLEX-1X4 CHIPLED_0805 CHIPLED_0805 R1210 M0805 M0805 ELFDRV1 stepper driver - electroFUN LTD 17 Board Dimensions ELFDRV1 - stepper driver board dimensions board dimensions ELFDRV1 stepper driver - electroFUN LTD 18 Assembled stepper driver on ELFSHL1 stepper shield driven by the vinciDuino. ELFDRV1 stepper driver - electroFUN LTD 19